The present invention relates to ink-jet heads for use in ink-jet recorders.
Recently, printers incorporating ink-jet recorders come into wide use as printers for personal computers and the like because of their high printing performance, handling ease, inexpensiveness and the like. There are a variety of ink-jet recorders of this type: some of them jet ink droplets utilizing pressure waves which are caused by bubbles formed in ink by thermal energy; some of them suck and jet ink droplets utilizing static electric power; some of them jet ink droplets utilizing pressure waves which are caused by vibrators such as piezoelectric elements, and the like.
Generally, the ink-jet recorders using piezoelectric elements comprise, for example, compression chambers communicating with ink-supply chambers and ink outlets communicating with the compression chambers, wherein the compression chambers are provided with vibration plates bonded with piezoelectric elements. In such a structure, when a given voltage is applied to the piezoelectric elements to expand or contract them, the piezoelectric elements vibrate bending themselves to compress the ink in the compression chambers, thereby jetting ink droplets from the outlets. Today, while color ink-jet recorders are coming into wide use, improvement on the printing performance, particularly high resolution and high-speed printing are demanded. Therefore, there are seen many trials to realize high resolution and high-speed printing by using multi-nozzle heads which are achieved by fine processing of ink heads. To finely process ink heads, it becomes necessary to miniaturize piezoelectric elements for use in jetting ink droplets.
In the meantime, the piezoelectric films of piezoelectric elements are formed by molding powder of PbO, ZrO2 and TiO2 into sheets and baking the molded sheets, and therefore, it is difficult to form piezoelectric thin films with a thickness of, for example, 20 xcexcm or less. For this reason, fine processing of piezoelectric films is accompanied by difficulties, which leads to difficulties in miniaturizing the piezoelectric elements. Further, in the above piezoelectric films formed by baking the powder, as their thickness is becoming smaller, the affection of the thickness on the grain boundary is becoming serious, so that sufficient piezoelectric characteristics can not be obtained. As a result, there is a problem in that the piezoelectric films formed by baking the powder can not provide sufficient piezoelectric characteristics to jet ink droplets when the thickness of the films is 15 xcexcm or less. Therefore, miniaturized ink heads having characteristics necessary for jetting ink droplets have not been realized.
Objects of the present invention are to provide structures for ink-jet heads having ink outlets which are formed at a high density, by developing thin film materials which have high piezoelectric characteristics in spite of very small thickness and forming piezoelectric films, vibration plates and the like therefrom with very small thickness for constituting piezoelectric elements, thereby making it possible to utilize fine processing techniques which have been applied to the field of the semiconductor processing, and also to provide methods for producing ink-jet heads having such structures.
A first ink-jet head according to the present invention comprises a body having ink outlets and compression chambers respectively communicating with each of the ink outlets, and piezoelectric vibration sections, each being provided on a part of each of the compression chambers and including a piezoelectric film containing Pb, Ti and Zr, and electrodes provided on both sides of the piezoelectric film, whereby each of the piezoelectric vibration sections generates flexural vibration to thereby jet ink droplets from each of the ink outlets, characterized in that the above piezoelectric film comprises a first layer having a perovskite structure containing Sr or Ba, and a second layer formed in contact with the first layer, having a perovskite structure containing Pb, Ti and Zr.
As mentioned above, by forming the second layer in contact with the first layer having a perovskite structure containing Sr or Ba, the second layer containing Zr can be formed thinner, having a higher quality and a larger piezoelectric constant. With this configuration, the first ink-jet head of the present invention can be made very small in size and light in weight.
A second ink-jet head according to the present invention comprises a body having ink outlets and compression chambers respectively communicating with each of the ink outlets, and piezoelectric vibration sections, each being provided on a part of each of the compression chambers and including a piezoelectric film containing Pb, Ti and Zr, and electrodes provided on both sides of the piezoelectric film, whereby each of the piezoelectric vibration sections generates flexural vibration to thereby jet ink droplets from each of the ink outlets, characterized in that the above piezoelectric film comprises a first layer and a second layer, each having a perovskite structure and being formed in contact with each other, and that the content of Zr in the first layer is smaller than that in the second layer.
As mentioned above, by composing the piezoelectric film of the first layer and the second layer which are formed in contact with each other, the second layer containing comparatively more amount of Zr can be formed thinner, having a good quality and a larger piezoelectric constant. With configuration, the second ink-jet head of the present invention can be made very small in size and light in weight.
A third ink-jet head according to the present invention comprises a body having ink outlets and compression chambers respectively communicating with each of the ink outlets, and piezoelectric vibration sections, each being provided on a part of each of the compression chambers and including a piezoelectric film containing Pb, Ti and Zr, and electrodes provided on both sides of the piezoelectric film, whereby each of the piezoelectric vibration sections generates flexural vibration to thereby jet ink droplets from each of the ink outlets, characterized in that the above piezoelectric film comprises a first layer containing no Zr and a second layer containing Zr, each having a perovskite structure and being formed in contact with each other. Thus, the second layer can have a better quality and a higher piezoelectric constant in comparison with the above second ink-jet head.
In the second and third ink-jet heads of the present invention, to form the first layers simply and at low temperatures, it is preferable for the first layers to contain La.
Also, in the first to the third ink-jet heads of the present invention, it is preferable for the second layers to have a Zr/Ti ratio within a range of 30/70 to 70/30 so as to further increase the piezoelectric constants of the above piezoelectric films.
Also, in the first to the third ink-jet heads of the present invention, it is more preferable for the above piezoelectric films to be single crystal so that the piezoelectric constants which the materials constituting the piezoelectric films inherently possess can be effectively utilized.
Also, in the first to the third ink-jet heads of the present invention, it is preferable for the above piezoelectric films to be formed with a thickness of 10 xcexcm or less so that the piezoelectric films can be finely processed.
Also, in the first to the third ink-jet heads of the present invention, it is more preferable for the above piezoelectric films to be formed with a thickness within a range of 1 to 3 xcexcm so that the piezoelectric films can be finely processed, and simultaneously that the ink heads can have sufficient ink-jetting powers and sufficiently reliable piezoelectric films. In this case, it is preferable for the first layers to be formed with a thickness within a range of 50 to 100 nm so that the second layers can be formed having better qualities. Thus, the piezoelectric constants of the piezoelectric films as a whole do not decrease.
Also, in the first to the third ink-jet heads of the present invention, by providing the above piezoelectric vibration sections with vibration plates, the piezoelectric vibration sections can easily generate flexural vibration. In this case, it is preferable that the above vibration plates are formed from at least one selected from the group consisting of Ni, Cr, Al and their oxides, Si, Si oxide, and high molecular compound.
Also, in the first to the third ink-jet heads of the present invention, each of the above piezoelectric vibration sections may generate flexural vibration by two piezoelectric films: that is, another piezoelectric film different from the above piezoelectric film is provided between each of the above electrodes, opposing to each other through an intermediate electrode layer. By the piezoelectric vibration section using two piezoelectric films as mentioned above, a larger vibration amplitude can be obtained as compared with the ink heads using vibration plates.
Also, in the first to the third ink-jet heads of the present invention, each of the second layers of the above piezoelectric films may be a piezoelectric matter which contains Nb and Sn and has antiferroelectricity.
Also, in the first to the third ink-jet heads of the present invention, the first layer of each of the above piezoelectric films may be formed as a layer in which the density of Zr is so distributed as to continuously increase along the thickness direction of the first layer, and which contacts the second layer at one side thereof having a higher Zr density.
Also, in the first to the third ink-jet heads of the present invention, it is preferable that the above electrode layers on both sides of each piezoelectric film are formed from Pt or Au. By doing so, the electrodes are not damaged by etchant, for example, when the piezoelectric film is finely processed by etching.
Also, in the first to the third ink-jet heads of the present invention, each of the bodies has a plurality of ink outlets and a plurality of compression chambers which are provided respectively corresponding to each of the ink outlets, respectively, and at least one of the electrodes provided on both sides of the piezoelectric film is divided into such patterns that can be separately disposed corresponding to the compression chambers, respectively, so that there can be provided an ink-jet head which comprises piezoelectric vibration sections, each corresponding to each of the compression chambers. With the structure as mentioned above, an ink-jet head which has a plurality of ink outlets formed at a very high density can be provided. In this case, the piezoelectric film may be divided into separate piezoelectric films which correspond to the compression chambers, respectively, and one of the above electrodes may be formed over the piezoelectric films divided. This can also provide an ink-jet head which has ink outlets formed at a high density. As described above, where the divided piezoelectric films are separately formed so as to correspond to the compression chambers, respectively, it is preferable that the width of each of the piezoelectric films is smaller than that of each of the compression chambers. Also, where the divided piezoelectric films are separately formed, a resin having such a low rigidity as not to prevent expansion or contraction of the piezoelectric film may be packed in the spaces between each of the piezoelectric films separated. By doing so, the reliability of the ink-jet head can be improved.
Also, in the first to the third ink-jet heads of the present invention, each of the piezoelectric vibration sections may be bonded at its periphery to the periphery of each compression chamber through a resin layer having elasticity and a thickness of 3 xcexcm or less. By doing so, deformation of the piezoelectric vibration section is prevented when it is bonded to the compression chamber, so that the production yield is increased and the reliability of the ink-jet head is improved.
It is preferable that the piezoelectric vibration section is bonded at its periphery to the periphery of the compression chamber through a mount which is formed from a ceramics, metal or resin. By doing so, the bonded portion can be distant from the piezoelectric vibration section, so that the above piezoelectric vibration section can be stably vibrated.
In the meantime, the method, according to the present invention, of producing an ink-jet head which comprises a body having ink outlets and compression chambers, each communicating with each of the ink outlets and having an opening at a part thereof; and piezoelectric vibration sections so provided as to close the openings of the compression chambers is as follows. The method comprises
a first step of forming piezoelectric vibration sections, each including a substrate and a piezoelectric film thereon, said step including a step of forming the piezoelectric film comprised of a first layer and a second layer, by forming, on the substrate, the first layer which has a perovskite structure containing Pb and Ti, and forming, on the first layer, the second layer which has a perovskite structure containing Zr, Pb and Ti,
a second step of facing the peripheries of the openings of the body to the peripheries of the piezoelectric vibration sections and bonding them to each other, and
a third step of removing the substrate after the bonding, and
the method is characterized in that the first layer is so formed as not to contain Zr, or as to contain a smaller amount of Zr than that contained in the second layer in the first step.
By the method of the present invention, the second layer which contains a comparatively larger amount of Zr can be formed with a small thickness, having a good quality and a large piezoelectric constant. Thus, according to the method of the present invention, there can be provided an ink-jet head which is made very small in size and light in weight.
In the method of the present invention, preferably, the sputtering process or the chemical vapor deposition (CVD) process is adopted so as to accurately form the first layer and the second layer having good qualities.
In the method of the present invention, by using an MgO substrate as the above substrate, the first layer and the second layer can be formed as single crystal layers. In this case, the substrate can be removed by etching using phosphoric acid in the third step.
In the method of the present invention, a silicone substrate or a glass substrate can be used as the above substrate. For the use of such a substrate, an ink-jet head can be produced at lower cost as compared with that produced by using an MgO substrate. In this case, the substrate can be removed by etching using a hydrofluoric acid solution or a potassium hydroxide solution in the third step.